Synthesis and characterization of 356-SiCp composites by stir casting and compocasting methods

Stir casting is one of the simplest ways of producing aluminum matrix composites. However, it suffers from poor incorporation and distribution of the reinforcement particles in the matrix. These problems become especially significant as the reinforcement size decreases due to greater agglomeration tendency and reduced wettability of the particles with the melt. Development of new methods for addition of very fine particles to metallic melts which would result in more uniform distribution and effective incorporation of the reinforcement particles into the matrix alloy is therefore valuable. In this work, 356-5%SiCp (volume fraction) composites, with average SiCp sizes of about 8 and 3 μm, were produced by injection of different forms of the reinforcement particles into fully liquid as well as semisolid slurries of 356 aluminum alloy and the effects of the injected reinforcement form and the casting method on distribution of the reinforcement particles as well as their porosity, hardness and impact strength were investigated. The results reveal that addition of SiC particles in the form of (Al-SiCp)cp composite powder and casting in semisolid state decreases the SiCp particle size, enhances the wettability between the molten matrix alloy and the reinforcements and improves the distribution of the reinforcement particles in the solidified matrix. It also increases the hardness and the impact energy of the composites and decreases their porosity.